Temperature dependence of the Maierndash;Saupe order matrix from2Hndash;NMR of fluorenehyphen;d10in the nematic, smectic A, B, and C phases@fa@f)

摘要

From2Hndash;NMR of perdeuterated fluorene (diphenylenemethanehyphen;d10) dissolved in 4hyphen;nhyphen;butyloxybenzylidenehyphen;4hyphen;nhyphen;octylaniline (4O.8) and in a mixture of 4O.8 with 4hyphen;4prime;hyphen;bishyphen;nhyphen;heptyloxyazoxybenzene (HOAB, 15.1 wt.thinsp;percnt;) we have measured each of the orientational order parameters of the Maierndash;Saupe order matrix and their temperature dependence in the nematic, smectic A, smectic B, and smectic C phases, respectively. The fluorenehyphen;d10molecule, being a rigid structure of known conformation and one which contains a sufficient number of differently oriented deuterated sites, allows for the complete determination of the order matrix in terms of the measured2Hndash;NMR spectral splittings. The results show: (1) The principal molecularzaxis (most ordered axis) is parallel to a direction which joins the centers of the six membered rings at all temperatures and in each phase studied; (2) nonlinearities are present in the temperature dependence of the ratios of the splittings and are a result of the temperature dependence of the elements of the order matrix,SzzandSxxndash;Syy, demonstrating that a change in molecular conformation is not necessarily the cause of such nonlinearities as suggested in the literature; (3) splitting ratio vs ratio plots are linear throughout all phases of 4O.8 and 4O.8+HOAB mixtures; (4) the degree of ordering of the solute (fluorene) is significantly reduced in the smectic phases, in confirmation of that suggested by other solute studies reported in the literature.